1. Field of the Invention
The present invention relates to a thermoplastic elastomer composition comprising a specific polyurethane and a specific aromatic vinyl compound-olefinic compound block copolymer and having excellent flexibility and resistance to abrasion, heat and oil.
2. Description of the Related Art
Thermoplastic polyurethanes, having excellent abrasion resistance and oil resistance, are used for hoses, belts, tubes and the like, but they have the drawbacks of poor hot water resistance and weather resistance and are hence their uses are limited. On the other hand, aromatic vinyl compound-olefinic compound block copolymers are excellent in rubber elasticity and hot water resistance, but their uses are also limited due to poor resistance to oil and abrasion and other drawbacks.
To eliminate the drawbacks of both thermoplastic polyurethanes and aromatic vinyl compound-olefinic compound block copolymers, blending of the two component has been attempted. However, sufficient properties have not been created by the blending, since thermoplastic polyurethanes and aromatic vinyl compound-olefinic compound block copolymers generally have poor compatibility with each other. For example BP 1581167 and Japanese Patent Application Laid-open No. 150464/1977 describe that molded articles having excellent tensile strength are obtainable from compositions comprising a polyether-based thermoplastic polyurethane and a block copolymer comprising a conjugated diene compound having a structure of X-Y-X (X: polymer block-comprising an aromatic vinyl compound; Y: polymer block comprising a conjugated diene compound) with at least 70% of the conjugated diene compound part being hydrogenated. The above compositions, however, have poor transparency due to poor compatibility of the two components.
It has also been attempted, in order to improve the compatibility of thermoplastic polyurethanes with aromatic vinyl compound-olefinic compound block copolymers, to add a dicarboxylic acid-modified block copolymer as a compatibility improving agent (see Japanese Patent Application Laid-open No. 115352/1981). However, this attempt can hardly be said to have achieved sufficient improvement.